Biological nitrogenases exhibit superior nitrogen fixation efficiency owing to their unique multi-iron metallocluster (Fe²⁺₃Fe³⁺₄M³⁺, M = Mo, V, Fe) coordinated by organic polypeptide. Herein, we design a kind of metal organic framework (MOF) photocatalyst, MIL-53(Fe^II/Fe^III) (MIL = Material from Institute Lavoisier), in which the Fe^II and Fe^III constitute the mixed-valence metalloclusters to mimic the Fe²⁺ active sites and high-valence metal ions in nitrogenases, respectively. Both the Fe^II and Fe^III are coordinated by organic ligands (terephthalic acid), which afford the electron transfer chains as well as the support of monodispersed Fe^II active sites. The Fe^III in MIL-53(Fe^II/Fe^III) is partly in-situ reduced into Fe^II by ethylene glycol (EG) via one-step solvothermal method, and the Fe^II/Fe^III ratio is regulated from 0.18:1 to 1.21:1 by varying the EG content. Our results show that the Fe^II/Fe^III ratio can significantly affect the photocatalytic activity and structure stability, and MIL-53(Fe^II/Fe^III)-1 with optimal Fe^II/Fe^III ratio (1.06:1) achieves the highest ammonia evolution rate up to 306 μmol h⁻¹ g⁻¹, nearly 10-fold higher than that of other framework-based materials, while remaining stable after 24 h irradiation. Such nitrogenase-like design in MIL-53(Fe^II/Fe^III) endows the efficient electron transfer, exposed active sites, and in particular rational synergy between the catalytic function and non-catalytic function. This work may open a new avenue to the rational design of nitrogen fixation photocatalysts based on framework materials.

生物固氮酶由于其独特的多铁金属簇簇（Fe ²⁺ ₃ Fe ³⁺ ₄ M ³⁺，M = Mo，V，Fe）而具有良好的固氮效率，该有机铁配体由有机多肽配位。本文中，我们设计了一种金属有机骨架（MOF）光催化剂，MIL-53（Fe ^II / Fe ^III）（MIL = Lavoisier研究所的材料），其中Fe ^II和Fe ^III构成了模拟的混合价金属簇合物固氮酶中的Fe ²⁺活性位点和高价金属离子。Fe ^II和Fe ^III由有机配体（对苯二甲酸）配位，这些配体提供电子转移链以及单分散Fe ^II活性位点的支持。通过一步溶剂热法通过乙二醇（EG）将MIL-53中的Fe ^III（Fe ^II / Fe ^III）部分原位还原为Fe ^II，并且将Fe ^II / Fe ^III的比例控制在0.18：1通过更改EG含量达到1.21：1。我们的结果表明，Fe ^II / Fe ^III比例可显着影响光催化活性和结构稳定性，而MIL-53（Fe ^II / Fe ^III具有最佳Fe ^II / Fe ^III比（1.06：1）的-1）达到最高的氨释放速率，达到306μmolh ^-1 g ^-1，比其他骨架材料高出近十倍，同时保持稳定照射24小时后。MIL-53（Fe ^II / Fe ^III）中的这种类似固氮酶的设计赋予了有效的电子转移，暴露的活性位点，尤其是催化功能和非催化功能之间的合理协同作用。这项工作可能为合理设计基于骨架材料的固氮光催化剂开辟新途径。